This invention relates generally to a screwdriver for driving collated screws which are joined together in a strip, and, more particularly, to a power screwdriver with a nose portion which renders the screwdriver adaptable for use in driving screws having different lengths and diameter screw heads.
Collated screwstrips are known in which the screws are connected to each other by a retaining strip of plastic material. Such strips are taught, for example, by U.S. Pat. No. 4,167,229 issued Sep. 11, 1979 and its related Canadian Patents 1,040,600 and 1,054,982 as well as U.S. Pat. No. 4,930,630, the disclosures of which are incorporated herein by reference. Screws carried in such screwstrips are adapted to be successively incrementally advanced to a position in alignment with and to be engaged by a bit of a reciprocating, rotating power screwdriver and screwed into a workpiece. In the course of the bit engaging the screws and driving it into a workpiece, the screw becomes detached from the plastic strip leaving the strip as a continuous length.
In the use of such collated screwstrips in screwdrivers, the strip serves a function of assisting in guiding the screw into a workpiece and, to accomplish this, the strip is retained against movement towards the workpiece. In the screwstrip, each screw to be driven has its threaded shaft threadably engaged in a threaded sleeve of the strip such that on the screwdriver engaging and rotating each successive screw, the screw turns within the sleeve which acts to guide the screw as it moves forwardly into threaded engagement into the workpiece. Preferably, only after the tip of the screw becomes engaged in the workpiece, does the head of the screw come into contact with the sleeves. Further, forward movement of the screw into the workpiece then draws the head downwardly to engage the sleeve and to rupture the sleeve by reason of the forward movement of the head with the strip retained against movement towards the workpiece. The sleeve preferably is configured to have fragile strips which break on the head passing through the sleeve such that the strip remains intact as a continuous length. Since the strip is a continuous length, on advancing the screwstrip with each successive screw to be driven, it necessarily results that portion of the strip from which each screw has been driven are also advanced to exit from the power screwdriver.
Known power screwdrivers for driving such collated screwstrips include U.S. Pat. No. 4,146,071 to Mueller et al, issued Mar. 27, 1976, and U.S. Pat. No. 5,186,085 to Monaceli, issued Feb. 16, 1993, the disclosure of which are incorporated herein by reference. Such known power screwdrivers include a rotatable and reciprocally moving screwdriver shaft which is turned in rotation by an electric motor. A screwdriving bit forms a forwardmost portion of the shaft for engaging the head of each successive screw as each screw is moved into a driving position, axially aligned under the screwdriver shaft.
An important aspect of such power screwdriver is the manner and accuracy with which the screws are advanced and positioned so as to be properly aligned axially under the screwdriver shaft for successful initial and continued engagement between the bit and the screwdriver head in driving a screw fully down into a workpiece. In the device of Mueller et al, a guide channel is provided through which the screwstrip is advanced. The guide channel is sized to receive screws of specific head size and minimum length. The guide channel is formed as an integral part of a sliding body which also carries other components of a screw advance mechanism including a feed pawl to engage the screwstrip and thereby advance successive screws in the screwstrip. The screws are successively advanced into position in alignment with the screwdriver shaft with the heads of the screws being urged into abutment with a stop which is to locate the screw head. The stop typically defines a radial extent of a boreway through which the shaft and screw head axially move as the screw is driven.
The shaft is axially movable in the boreway in a reciprocal manner to engage the screw and drive it into a workpiece. After each screw is driven the shaft retracts and a subsequent screw carried on the screwstrip is advanced sideways into the boreway, engaging the stop so as to be aligned under the shaft.
Known power drivers for collated screws have a slide body which is reciprocally slidable relative a housing in a normal cycle of operation. Known screw advance mechanisms are coupled between the slide body and housing to translate relative movement of the slide body and housing into a cyclical cycle of advance of the screwstrips.
Known screw advance mechanisms suffer the disadvantage that they are complex and typically involve a number of components. For example, in the device of Mueller et al, U.S. Pat. No. 4,146,071, the advance mechanism comprises three interrelated lever members together with a camming roller which cams on a camming surface. A primary spring biases the slide body to an extended position relative the housing. A secondary spring biases the lever members to urge the roller into the camming surface and the screwstrip towards the fully advanced position. The secondary spring has the disadvantage of being relatively strong and requiring substantial additional forces for operation so as to telescope the slide body into the housing and overcome the additional frictional forces developed between the camming roller and the camming surfaces.
Known screwstrip advance mechanisms are unduly complex, expensive to manufacture, cumbersome, bulky and inconsistent in their features with a lightweight tool of minimum size.
To at least partially overcome these disadvantages of the prior art, the present invention provides a screwdriver for driving collated screws including a slide body coupled to a housing for reciprocal displacement in a cycle including a retraction stroke and an extension stroke, a lever pivotably mounted to the slide body carries at one end a cam pin received in a cam slot in the housing with the other end of the lever advancing successive screws in the screwstrip, the cam slot having first and second camming surfaces for selective engagement by the cam pin to vary the relative positioning of the lever to be different for the same positions of the slide body in the housing in the retraction strokes than in the extension stroke.
An object of the present invention is to provide a simplified arrangement for translating relative positioning of the slide body and the housing into positioning of the screw advance mechanism, yet permitting for different positions in an extension stroke versus a retraction stroke.
Another object is to provide in an attachment for driving collated screws an enhanced sequencing of relative positioning of the screw to be driven, the next screw to be driven and the mandrel in cyclical steps of advancing and driving each screw.
Accordingly, in one aspect the present invention provides an apparatus for driving with a power driver a screwstrip comprising threaded fasteners, such as screws or the like, which are joined together in a strip comprising:
a housing;
an elongate driver shaft for operative connection to a power driver for rotation thereby and defining a longitudinal axis;
a slide body coupled to the housing for displacement parallel to the axis of the driver shaft between an extended position and a retracted position;
the slide body having a guide channel for said screwstrip transverse to the axis,
a shuttle carried on the slide body movable relative the slide body transverse to the axis towards and away from the axis,
the shuttle carrying pawl means for. engagement with the screwstrip to advance the screwstrip with movement of the shuttle towards the axis to place successive of the fasteners into axial alignment with the driver shaft for driving by the driver shaft,
a lever having a first end coupled to the shuttle and a second end coupled to the housing whereby movement of the slide body axially relative the housing (a) towards the extended position moves the shuttle towards the axis and (b) away from the extended position moves the shuttle away from the axis,
the lever pivotably mounted on the slide body intermediate its first and second ends;
the housing having an elongate cam slot having side-by-side first and second camming surfaces,
the second end of the lever carrying a cam pin member slidably engaged in the cam slot between the first and second camming surfaces;
the slide body moving relative the housing in a cycle of operation in which the slide body moves in a retracting stroke from the extended position to the retracted position and then moves in an extending stroke from the retracted position to the extended position,
in at least some identical relative positions of the slide body and housing, the pin member engages the first camming surface in the retracting stroke and the second camming surfaces in the extending stroke such that the lever places the shuttle at different positions relative the identical positions of the slide body and housing in a retracting stroke than in an extending stroke.